Vehicle airbag restraint systems are widely used to prevent or reduce injury to occupants involved in vehicle collisions. An airbag restraint system consists of a collision sensing device, an inflatable bag, and an inflator. The inflatable bag and inflator are commonly housed in a steering wheel or dashboard in front of the occupants. Upon collision, the collision sensing device outputs a signal to activate the inflator. Gases are rapidly released from the inflator to fill the bag, causing the bag to burst from the steering wheel dashboard container into a fully inflated restraining cushion. The process is nearly instantaneous as the bag is inflated during the brief time period following collision but before the occupant is propelled forward into the steering wheel or dashboard during a crash.
In recent vehicle models, airbag restraint systems are standard equipment. They typically include both driver-side airbags and passenger-side airbags. In some vehicles, such as minivans, the airbag restraint systems also include side airbags to protect passengers, such as children, from broadside collisions.
This invention concerns the inflator portion of the airbag restraint system. The inflator includes a canister, a pressurized gas, and an initiator. The canister defines a pressurized gas chamber and a diffuser. The gas chamber stores a liquefied gas or gas (e.g., nitrogen, argon, oxygen) under pressure. A burst disk separates the gas chamber from the diffuser. The initiator is mounted within the canister and electrically activated upon receipt of the signal from the collision sensing device. The initiator begins the inflation process which entails rupturing the burst disk to release the pressurized gas from the chamber, out through the diffuser, and into the bag.
This invention is more specifically directed to the canister. A conventional canister comprises a multi-piece assembly having a separate gas chamber, a separate diffuser that is welded or secured to the gas chamber, and various end pieces and caps. The burst disk is often another separate piece welded or sealed between the chamber and diffuser. Each of these pieces are typically formed of different materials. For instance, an inflator manufactured by Morton International employs a low carbon steel for the canister body, and a nickel-based alloy (e.g., Iconel.TM.) for the burst disk. Other examples of multi-piece canisters can be found in UK Patent Application GB 2,270,742A to Blumenthal and U.S. Pat. No. 3,968,980 to Hay.
Multi-piece canisters have drawbacks. Each component and piece requires separate manufacturing, resulting in higher costs of materials and manufacturing. Additionally, the multi-piece assemblies typically require multiple welds which results in longer assembly time and expense. Also, multiple welding steps typically result in higher assembly scrap rates.
U.S. Pat. Nos. 3,966,225 and 4,018,457, both to Marlow, show inflators that employ an integrated canister in which the gas chamber is integrally formed with the diffuser. However, the canister described in these patents has a special structural design that is not conducive to easy and mass manufacturing practices. The gas chamber portion of the canister is a bottle-like shape with a wide diameter body tapering to a narrow diameter neck. The tapered neck acts as a mount for a propellant storage means. The diffuser portion of the canister is a small diameter extension which projects from the wide diameter body in an opposite direction from the tapered neck portion of the gas chamber.
As a result of this particular shape, the Marlow canister is difficult to manufacture. Several steps are required to form the bottle-like gas housing component and the small diffuser.
Accordingly, there is a need for an improved integrated canister that is both inexpensive and easy to manufacture.